1. Field of the Invention
This invention is related to a method for producing a porous thin film with variable transmittance, and more particular to a porous thin film produced by means of water absorption characteristic of salt which can change the light transmittance of the porous thin film under a dry state and a hydrous state.
2. Description of Related Art
The conventional optical transmittance and reflectance control technology is to add an electric field to a general liquid crystal layer made of a liquid crystal material in the liquid crystal display, which twists the liquid crystal molecules and changes the polarization direction of a light propagation, and then the polarization direction of a light propagation is filtered by the polarizer, so as to control the transmittance.
For example, photochromic lenses are plated a compound thin film via a glass lens. The compound thin film produces a chemical reaction by ultraviolet radiation, and thereby the chemical structure is changed, resulting in the corresponding change of the optical transmittance, reflectance or absorption rate.
In another example, the electrochromic technology uses an added electric field to allow the ions to be injected into a photochromic material, which changes the color of the photochromic material, and further changes light transmittance, reflectance and absorption rate of the photochromic material. The electrochromic technology can be applied in the areas of green energy industry and electronic goods, such as the electrochromic glasses used in construction materials, which are used to regulate the light transmittance between outdoors and indoors; and the electrochromic technology can be also applied to the flexible electronic paper.
However, in order to advocate the green energy technology, the above mentioned control technology of the liquid crystal polarization and the electrochromic technology need external power to work, which needs more which needs more power while in use, and the manufacturing costs of both technologies are also high.
The transmittance change in the compound thin film on the photochromic lenses is only a change in color, the compound thin film still belongs to a transparent film, so that its application range is limited. Therefore, how to develop a thin film with low usage cost, low manufacturing cost and more than 50% transmittance change are the lessons the industry needs to resolve.